Shock absorber assembly

ABSTRACT

A shock absorber assembly includes a motion damping means that is filled with a fluid in operation and has a pair of relatively moveable parts ( 12, 14 ) and valve means ( 26 ) permitting flow of the fluid between the parts. The parts comprise a first part ( 12 ) and a second part ( 14 ) in which the first part is receivable whereby the parts are arranged for relative retracting and extending movement during which fluid is forced through the valve means ( 26 ) at respective predetermined controlled flow rates so as to dampen the movement. The relatively moveable parts contain respective primary chambers ( 24, 29 ) for the fluid. The first part is substantially smaller in cross-section than the second part to define an intermediate chamber ( 52 ) about the first part within the second part. Lateral port means ( 56 ) communicates the intermediate chamber ( 52 ) and the primary chamber ( 24 ) of first part ( 12 ). The flows at respective predetermined controlled flow rates are limited to respective flows (i) directly from the primary chamber ( 24 ) of the first part ( 12 ) to the primary chamber ( 29 ) of the second part ( 14 ) and (ii) via the intermediate chamber ( 52 ) and lateral port means ( 56 ) from the primary chamber ( 29 ) of the second part ( 14 ) to the primary chamber ( 24 ) of the first part ( 12 ).

FIELD OF THE INVENTION

This invention relates generally to shock absorbers but is particularlyuseful for shock absorber assemblies in vehicle suspension systems,especially in heavy duty applications such as trucks and industrialvehicles, and off-road racing vehicles. The invention will primarily bedescribed in this context in this specification but it will beunderstood that the invention is broadly applicable to shock absorbersin general. Other applications include motorcycles, industrialmachinery, industrial switch gear systems, and suspension systems forseats, particularly vehicle seats, truck cab suspensions or the like.

BACKGROUND ART

Vehicle suspension systems fall into a variety of broad sub-classesaccording to the mechanism by which motion is damped and smoothed. Onesuch sub-class relies on a fluid system in which a suitable, typicallysubstantially incompressible, fluid is forced through one or more valvedevices at one or more predetermined controlled rates so as to dampen arelative movement, typically a reciprocal telescopic movement, betweentwo components. The valve devices are typically double-acting and so arerelatively complex, requiring separate ducting and separate one-wayvalving for each direction of flow. Resiliently deformable or axiallymoveable shim packs are a typical form of one-way valving, while flowpassages for the two directions of flow are commonly accommodated in asingle valve body.

It is an object of the invention to provide an improved shock absorberassembly of the type having a fluid damping mechanism.

SUMMARY OF THE INVENTION

The invention provides a shock absorber assembly including a motiondamping means that is filled with a fluid in operation and has a pair ofrelatively moveable parts and valve means permitting flow of the fluidbetween the parts, the parts comprising a first part and a second partin which the first part is receivable whereby the parts are arranged forrelative retracting and extending movement during which fluid is forcedthrough said valve means at respective predetermined controlled flowrates so as to dampen said movement.

The relatively moveable parts contain respective primary chambers forthe fluid and the first part is substantially smaller in cross-sectionthan the second part to define an intermediate chamber about the firstpart within the second part. There is further included lateral portmeans communicating the intermediate chamber and the primary chamber ofthe first part. The aforesaid flows at respective predeterminedcontrolled flow rates are limited to respective flows (i) directly fromthe primary chamber of the first part to the primary chamber of thesecond part and (ii) via said intermediate chamber and lateral portmeans from the primary chamber of the second part to the primary chamberof the first part.

Preferably, the first and second parts comprise telescopicallyinterengaged tubes respectively of relatively smaller and largerdiameter. Advantageously, the valve means is provided in a valve bodyfixed at an inner end of the tube comprising the first part. The lateralport means then conveniently comprises a plurality of spaced individualports in the tube comprising the first part.

Preferably, the lateral port means is positioned whereby, duringextending movement, the lateral port means is covered near the end ofthe movement, whereby fluid in the intermediate chamber cushions furtherextending movement.

The assembly may further include respective sets of shims in partdetermining the respective predetermined controlled flow rates andfurther determining the respective directions of flow.

The assembly preferably further includes pressurised-gas cushioningmeans including structure defining a first cavity for storing apressurised gas and a second cavity for storing a fluid under pressure,and a floating piston sealingly separating the cavities, wherein thesecond cavity is in fluid flow communication with the motion dampingmeans. Further preferably, said movement is such that when the aforesaidparts relatively extend, fluid is caused to flow from the second cavityof the pressurised-gas cushioning means to the damping means whereby gaspressure in the first cavity moves the floating piston to reduce the gaspressure in the first cavity, and when the parts relatively retract,fluid is caused to flow from the damping means to the second cavitywhereby to move the floating piston to increase the gas pressure of thegas in the first cavity.

In one embodiment, the first part of the motion damping means and theaforesaid structure of the pressurised-gas cushioning means are integralwhereby the second cavity and the primary chamber of the first partcomprise a single chamber. For example, the first part of the motiondamping means and the structure of the pressurised-gas cushioning meansare provided by a single tube.

In an alternative embodiment, the pressurised-gas cushioning means andthe motion damping means are substantially separate units and a conduitis provided for the fluid flow communication between the motion dampingmeans and the second cavity. In one arrangement, this conduit is betweenthe primary chamber of the first part of the motion damping means andthe second cavity. Alternatively, the conduit may be between the primarychamber of the second part of the motion damping means and the secondcavity.

The valve means may be such that the respective predetermined controlledflow rates in the respective directions are different whereby to varythe damping characteristics according to whether the aforesaid movementis relative retracting or extending movement.

The assembly may further include cooling means for reducing thetemperature of the assembly during operation.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described, by way of example only,with reference to the accompanying drawings, in which:

FIG. 1 is a fragmentary cross-sectional view of a shock absorberassembly according to a first embodiment of the invention, incorporatingpressurised-gas cushioning means in an integrated telescopic structure;and

FIG. 2 is a similar view of a second embodiment of the invention inwhich the pressurised-gas cushioning means is provided in a separatehousing; and

FIG. 3 is a cross sectional view taken along line 3-3 in FIG. 2.

DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The shock absorber assembly illustrated in FIG. 1 is an integrated shockabsorber unit 10 that includes pressurised-gas cushioning means 11 andwould typically be one of a number of such units forming auxiliarycomponents of a suspension system in a vehicle. The units may be actingindividually or be linked in a fluid circuit to provide a managed andbalanced suspension response.

Shock absorber unit 10 has a first cylindrical tube 12 received within asecond cylindrical tube 14 so that the two tubes constitute mutuallyreciprocably moveable parts. Tube 12 is connected to tube 14 through ahead 13 of tube 14 that includes a sealing configuration 17 about tube12.

Tube 12 incorporates gas cushioning means 11 and to this end isprovided, in this case at its outboard or proximal end, with a fillingvalve 18 for introducing gas, such as nitrogen or similar, underpressure into the tube 12 to fill a first cavity or chamber 20 locatedat or towards the proximal end of tube 12 for storing gas underpressure. A double sided floating piston 22 or other suitable separatingelement, eg. a diaphragm or the like, is provided intermediate the twoends of tube 12. The first chamber 20 is formed between filling valve 18and piston 22. A second chamber 24 is formed between piston 22 and theinboard or distal end of tube 12. Hydraulic fluid fills the secondchamber 24 of tube 12.

A double acting valve arrangement 26 is provided in a valve body 25 ator towards the inboard or distal end of tube 12. Valve body 25 slidablyengages the cylindrical interior surface 15 of tube 14 and separateschamber 24 from larger chamber 29 defined within tube 14 between valvebody 25 and an end cap 27 of tube 14. Elsewhere in this specification,chambers 24, 29 are referred to as the primary chambers of tubes 12, 14.

Valve arrangement 26, and tubes 12, 14 form motion damping means filledwith hydraulic fluid in operation. Valve body 25 moves through thehydraulic fluid or the hydraulic fluid moves through the valve body inaccordance with corresponding movement of tube 12, depending on whetherthe valve body 25 is fixed or free to move. Preferably, the valvearrangement is fixed about the end of tube 12 by transverse fasteningscrews 27.

Tube 12 is substantially smaller (an internal cross-sectional area ratioof the order of 1:12) in cross-section than tube 14 so that anintermediate variable-volume annular chamber 52 is provided within tube14 and about tube 12 between head 13 and valve body 25. Fluidcommunication between chamber 24 and chamber 52 is provided by a ring ofbleed ports 56 in tube 12, displaced axially from valve body 25.

The individual valving of valve arrangement 26 is such to allow fluid toflow in one direction at one rate when tube 12 moves in a first axialdirection and to flow in the opposite direction at a second rate whentube 12 moves in the opposite direction. The rate of movement of fluidthrough the valving is dependent on the number, size and arrangement ofthe apertures, ports or ducts 40, 50, and on the flow control elements,in this case shim packs 54, 55, forming the actual valving within valvearrangement 26.

More specifically, when the tubes 12, 14 relatively retract, ie., duringcompression, fluid is forced into chamber 52 via a ring of outer ducts50 parallel to the axis of the valve body 25 within and adjacent theperiphery of the valve body, against annular non-return shim pack 54.Shim pack 54 is retained about a rebated end portion 12a of tube 12between valve body 25 and a peripheral shoulder 53 on the tube. Fromchamber 52, fluid flows into chamber 24 via ports 56. On extension orrebound, shim pack 54 closes ducts 50, and fluid flows from chamber 24into chamber 29 via a ring of oblique ports 40 of valve arrangement 26,controlled by disc-like non-return shim pack 55. Shim pack 55 isretained on the outer face of valve body 25 by an axially located bolt51. In other embodiments, shim packs 54, 55 may be substituted by otherforms of one-way or non-return valve, eg. spring-loaded ball valves.

When head 13 passes ports 56, the residual fluid in chamber 52 cushionsfurther relative motion of tubes 12, 14, and thereby provides hydraulictop-out.

Both ends of integrated unit 10 are provided with suitable fittings suchas eye 45 to enable the unit to be located in place as part of thesuspension system of a motor vehicle. It is to be noted that anysuitable fitting can be provided at either or both ends of this form ofthe unit. If necessary or desirable, one or both of tubes 12, 14 can beprovided as desired with cooling fins to cool component 10 in use, orwith outer cooling jackets for receiving recycled coolant to coolcomponent 10. Additionally or alternatively, the outer surface ofdamping tube 14 (especially about chamber 52) is provided withremovable, replaceable and/or interchangeable air cooling fins locatablearound the outside of the outer wall of tube 14 for increased cooling ifrequired.

In operation of this form of the shock absorber unit, the outboard endof damping tube 14 is fixedly located to suspension components of thewheel of a motor vehicle, or to another component which is connectedeither directly or indirectly to a road wheel of the vehicle, so as toact as a shock absorber for the suspension component. Thus, tube 14moves in accordance with substantially vertical movement of the wheelover bumpy or rough terrain or the like. The outboard end of tube 12 isconnected to the body work of the motor vehicle or other fixed componentand is thus fixed in place.

In operation when a road wheel encounters a bump in the form of a crestor rise or similar, damping tube 14 is forced by the suspension of thewheel towards tube 12 so that the length of the combined component 10 isreduced. In turn, the inboard end of tube 12 is forced further into thebody of tube 14, thereby pumping hydraulic fluid from within tube 14through valve arrangement via ducts 50 into chamber 52, then via ports56 into chamber 24. As the volume of fluid being forced into chamber 24increases, piston 22 travels axially along the inside wall of tube 12towards the outboard or proximal end of this tube thereby furthercompressing the gas in chamber 20 and increasing the internal pressurewithin component 10. This in turn offers increasing resistance tofurther movement of tube 14, thus limiting the amount of travel of tube14 which in turn limits the amount of travel of the road wheel in asubstantially vertically upwards direction.

When the road wheel returns to its normal position, such as for example,when rebounding or when encountering a trough or crest in the road, thelength of integrated unit 10 is increased by tubes 12 and 14telescopically expanding with respect to each other, thereby allowingfluid to move from chamber 24 into tube 14 via ducts 40. This reducesthe amount of fluid in chamber 24, allowing piston 22 to move under theincreased gas pressure of the compressed gas stored in chamber 20 whichin turn reduces the compression or gas pressure of the gas in chamber20. Further fluid is pumped into tube 14 until all of the pressuresequilibrate. The rate at which fluid can flow through valve arrangement26 limits the amount of travel of the road wheel in the substantiallyvertically downward direction.

The arrangement of valve body 25 so that fluid flow between chambers 24,29 in one direction is via annular intermediate chamber 52, instead ofdirectly between chambers 24 and 29 in both directions, permits a muchclearer and simpler construction of the valve body. The two sets ofmultiple, angularly-spaced ducts 40, 50 can be radially separated ratherthan entwined in a common radial zone, which both simplifiesconstruction and improves flow lines. Further simplification arisesbecause the intake ports of each duct set are automatically clear of theshim pack fur the other duct set because of the radial spacing. Theresulting improved fluid flow lines reduces heat build-up at thevalving, an important benefit in heavy duty applications such asoff-road vehicle racing.

A further benefit of the illustrated construction is that the cleanseparation of the duct and shim packs for the two directions of fluidflow permits better rebound control because of the radially distinctflow locations, and additionally permits incorporation of a cushioninghydraulic top out on the extension stroke in the manner already noted.

The presence of the high pressure gas cushioning features provides theability to adjust the gas pressure to an appropriate level and so reducethe incidence of “bottoming out” of the suspension system. Operationalparameters can also be adjusted by modifying the shim packs or varyingthe cross-sectional sizes and/or numbers of ducts 40, 50 and ports 56.

FIG. 2 depicts a second embodiment 110 into which the gas cushioningmeans is provided as a separate unit 111 in housing 100. Elements ofthis embodiment having counterparts in the first embodiment areindicated by like same reference numerals preceded by a “1”. Tube 12 ofthe first embodiment has been replaced by a solid shaft 105 axiallybored at one end to define a tubular segment 112 and chamber 124. Ports156 are provided in this tubular segment 112.

Gas cushioning unit 111 comprises a generally cylindrical housing 100with closed ends 101, 102, divided internally by a floating piston 122into a hydraulic fluid or oil chamber 104 and a pressurised-gas chamber120. Gas filling valve 118 for chamber 120 is provided in cylinder end101. Chamber 104 is in open flow communication with primary fluidchamber 129 via duct 106, which opens into chamber 129 at its axial endopposite valve body 125.

It will of course be appreciated that, while FIG. 2 shows housing 100 inclose proximity to tube 114, this is by no means necessary. Housing 100might be alternatively located at a remote location, and duct 106 mightthen be a flexible line linking the two chambers 104, 129.

This embodiment functions in a similar manner to the first embodiment.However, the provision of the high-pressure gas cushioning in a largerdiameter auxiliary chamber allows a more effective rising rate duringoperation, especially compared to conventional shock absorbers where thepiston moves very little and so there is little change in rising rate.

In the second embodiment 110, rebound compression adjustment can beachieved by modifying shim packs 154, 155, or compression can beincreased by varying the gas pressure in chamber 120 using filling valve118. Compression can be adjusted by using adjuster restrictor 160 tovary the flow through duct 106. Rebound is adjustable by axial movementof internal end cap 170 in chamber 124, utilising rod 172, to restrictflow through ports 156.

The invention claimed is:
 1. A shock absorber assembly including: amotion damping means that is filled with a fluid in operation and has apair of relatively moveable parts and valve means permitting flow ofsaid fluid between said parts, said parts comprising a first part and asecond part in which the first part is receivable whereby the parts arearranged for relative retracting and extending movement during whichfluid is forced through said valve means at respective predeterminedcontrolled flow rates so as to dampen said movement; wherein saidrelatively moveable parts contain respective primary chambers for saidfluid and said first part is substantially smaller in cross-sectioncross section than said second part to define an intermediate chamberabout the first part within the second part; and wherein there is thefirst part further included includes lateral port means communicatingsaid intermediate chamber and said primary chamber of the first part;and wherein said flows at respective predetermined controlled flow ratesare limited to respective flows (i) through a piston directly from theprimary chamber of the first second part to the primary intermediatechamber of the second part and (ii) via from said intermediate chamberand through the lateral port means of the first part into the primarychamber of the first part, then through the piston from the primarychamber of the second first part to the primary chamber of the firstsecond part; characterized in that said and wherein the valve meansincludes peripheral compression ports and a central at least one reboundport radially separated inwardly from the peripheral compression portssuch that the differences in flow rates of said compression and reboundports provides differential fluid flow rates for the compression andrebound stroke said relative retracting and extending movements of thefirst and second parts of said assembly.
 2. A shock absorber assemblyaccording to claim 1 wherein said first and second parts comprisetelescopically interengaged tubes respectively of relatively smaller andlarger diameter.
 3. A shock absorber assembly according to claim 2wherein said valve means is provided in a valve body fixed at an innerend of the tube comprising said first part.
 4. A shock absorber assemblyaccording to claim 3 wherein said lateral port means comprises aplurality of spaced individual ports in said tube comprising said firstpart.
 5. A shock absorber assembly according to claim 3 wherein saidlateral port means is positioned whereby, during said extendingmovement, the lateral port means is covered near the end of themovement, whereby fluid in said intermediate chamber cushions furtherextending movement.
 6. A shock absorber assembly according to claim 2wherein said lateral port means comprises a plurality of spacedindividual ports in said tube comprising said first part.
 7. A shockabsorber assembly according to claim 6 wherein said lateral port meansis positioned whereby, during said extending movement, the lateral portmeans is covered near the end of the movement, whereby fluid in saidintermediate chamber cushions further extending movement.
 8. A shockabsorber assembly according to claim 2 wherein said lateral port meansis positioned whereby, during said extending movemnet, movement thelateral port means is covered near the end of the movement, wherebyfluid in said intermediate chamber cushions further extending movement.9. A shock absorber assembly according to claim 1, further includingpressurized-gas cushioning means including structure defining a firstcavity for storing a pressurized gas and a second cavity for storing afluid under pressure, and a floating piston sealingly separating saidcavities, wherein said second cavity is in fluid flow communication withsaid motion damping means.
 10. A shock absorber assembly according toclaim 9, wherein said movement is such that when said parts relativelyextend, fluid is caused to flow from said second cavity of thepressurized-gas cushioning means to the damping means whereby gaspressure in said first cavity moves the floating piston to reduce thegas pressure in the first cavity, and when said parts relativelyretract, fluid is caused to flow from the damping means to said secondcavity whereby to move the floating piston to increase the gas pressureof the gas in the first cavity.
 11. A shock absorber assembly accordingto claim 10 wherein said first part of the motion damping means and saidstructure of the pressurized-gas cushioning means are integral wherebysaid second cavity and said primary chamber of the first part comprise asingle chamber.
 12. A shock absorber assembly according to claim 10wherein said pressurized gas cushioning means and said motion dampingmeans are substantially separate units and a conduit is provided forsaid fluid flow communication between the motion damping means and saidsecond cavity.
 13. A shock absorber assembly according to claim 9,wherein said first part of the motion damping means and structure of thepressurized-gas cushoning cushioning means are integral whereby saidsecond cavity and said primary chamber of the first part comprise asingle chamber.
 14. A shock absorber assembly according to claim 13,wherein said first part of the motion damping means and said structureof the pressurized-gas cushioning means are provided by a single tube.15. A shock absorber assmebly assembly according to claim 1, whereinsaid pressurized-gas cushioning means and said motion damping means aresustantially substantially separate units and a conduit is provided forsaid flow communication between the motion damping means and said secondcavity.
 16. A shock absorber assembly according to claim 15 wherein saidconduit is between the primary chamber of the first part of the motiondamping means and said second cavity.
 17. A shock absorber assemblyaccording to claim 15 wherein said conduit is between the primarychamber of the second part of the motion damping means and said secondcavity.
 18. A shock absorber assembly according to claim 1, wherein thevalve means is such that said respective predetermined controlled flowrates in the respective directions are different whereby to vary thedamping characteristics according to whether said movement is relativeretracting or extending movement.
 19. A shock absorber assemblyaccording to claim 1 including respective shim packs in part determiningsaid respective predetermined controlled flow rates and furtherdetermining the respective directions of flow.
 20. A shock absorberassembly including: a motion damping means that is filled with a fluidin operation and has a pair of relatively moveable parts and valve meanspermitting flow of said fluid between said parts, said parts comprisinga first part and a second part in which the first part is receivablewhereby the parts are arranged for relative retracting and extendingmovement during which fluid is forced through said valve means atrespective predetermined controlled flow rates so as to dampen saidmovement; wherein said relatively moveable parts contain respectiveprimary chambers for said fluid and said first part is substantiallysmaller in cross-section than said second part to define an intermediatechamber about the first part within the second part; and wherein thefirst part further includes lateral port means communicating saidintermediate chamber and said primary chamber of the first part; andwherein said flows at respective predetermined controlled flow rates arelimited to respective flows: (i) through a piston directly from theprimary chamber of the second part to said intermediate chamber via anouter ring of compression ports in the piston and (ii) from saidintermediate chamber to the primary chamber of the second part via thelateral port means in the first part, the primary chamber of the firstpart and at least one rebound port in the piston, said at least onerebound port being radially separated inwardly from the outer ring ofcompression ports such that the differences in flow rates of saidcompression and rebound ports provide differential fluid flow rates forsaid relative retracting and extending movements of the first and secondparts of said assembly.
 21. A shock absorber assembly as claimed inclaim 20, further comprising a pressurized-gas cushioning means.
 22. Ashock absorber assembly as claimed in claim 21, wherein the pressurizedgas cushioning means is in fluid communication with the primary chamberof the second part, and wherein said fluid flow during said relativeretracting movement of the first and second parts additionally comprisesfluid flow from the primary chamber of the second part to thepressurized-gas cushioning means, and said fluid flow during saidrelative extending movement of the first and second parts additionallycomprises fluid flow from said pressurized gas cushioning means to theprimary chamber of the second part.
 23. A shock absorber assembly asclaimed in claim 21, wherein the pressurized gas cushioning means isintegral to the first part, and wherein said fluid flow during saidrelative retracting movement of the first and second parts additionallycomprises fluid flow from the primary chamber of the second part to thepressurized-gas cushioning means via the outer ring of compressionports, the intermediate chamber and the lateral port means, and saidfluid flow during said relative extending movement of the first andsecond parts further comprises fluid flow from the pressurized gascushioning means through the at least one rebound port to the primarychamber of the second part.
 24. A shock absorber assembly as claimed inclaim 20 wherein said valve means includes respective shim packs in partdetermining said respective predetermined controlled flow rates andfurther determining the respective directions of flow.